1. Field of the Invention
The present invention relates to scientific calculators, and more particularly to a scientific calculator capable of converting one unit into another.
2. Description of the Prior Art
Conventional scientific calculators include a calculator capable of converting a numeric value entered with a certain unit into a numeric value with a different unit. For example, some calculators designed for scientific calculations are provided with a unit conversion function to perform a conversion calculation of physical units. Some calculators designed for travelers are capable of converting one currency unit into another.
Since scientific calculators, which are a small size electronic device, have only a limited number of keys, unit conversion functions are incorporated in keys for entering numeric values with the result that the unit conversion functions are performed by operating keys for entering numeric values 0 to 9 following the depression of a secondary function designation key ([2ndf] key).
FIG. 7 is a view illustrating an external configuration of a scientific calculator in the prior art. As shown in FIG. 7, this method permits storing 10 function units with a combination of [2ndf] key and numeric value keys.
Referring to FIG. 7, Reference Numeral 81 designates a display unit of the calculator, 81a a numeric value display unit for displaying numeric values, and 81c a [2ndf] symbol indicating the selection of a secondary function.
Reference Numeral 82 designates a key input unit, 82a a unit conversion calculation key assigned as the secondary function of numeric value entering keys, which includes such keys as [in.fwdarw.cm], and [cm.fwdarw.in] keys, 82b a [2ndf] key for designating the secondary function, 82c a [ON/C] key for clearing calculations or turning on the calculator that has been turned off, 82d a key for performing function calculations, which includes such keys as [sin], [cos] keys and the like, 82e an argument key for entering numeric values, which includes such keys as [0] key through [9] key, 82f a key for designating the kind of calculations such as addition, subtraction, multiplication and division, which includes such keys as [+], [-], [.times.], and [.div.] keys, 82g a key for performing memory calculations, which includes such keys as [X.fwdarw.M], [RM], [M+] keys, and 82h a [=] key for performing calculations such as addition, subtraction, multiplication and division.
FIG. 8 is a view illustrating a calculation example of unit conversion by a conventional scientific calculator. In the example shown in FIG. 8, the inch unit in 1.23 inches is converted into the centimeters.
Step 901: Step 901 clears the content of the calculator by operating the [ON/C] key.
Step 902: Step 902 enters 1.23 whose unit is to be converted.
Step 903: Step 903 selects the secondary function. In this operation, the secondary function described above the key switch will be made effective.
Step 904: Step 904 performs a conversion calculation. Operating [0] key performs the calculation of [in.fwdarw.cm], which is provided as a secondary function of [0] key.
However, it is impossible to assign many calculation conversion functions to numeric value entering keys whose number is restricted. Consequently, incorporating conversion calculation functions in excess of the number of numeric value entering keys has a drawback which demands either assigning the conversion functions to other keys than numeric value entering keys or increasing the number of functions assigned to numeric value entering keys as a tertiary or a quaternary function.
Thus, in either case, conventional calculators have a drawback that the number of conversion calculations depends on the number of keys.
As additional related art of the present invention a small size electronic calculator is known as disclosed in Japanese Laid-Open Patent Publication No. SHO 58-178459/1983. The calculator provides a plurality of unit keys and a memory for storing conversion values between units designated by the unit key to perform initialization of the conversion value to be stored in the memory by operating a unit key and to perform the unit conversion processing by using the conversion value stored in the memory. A unit conversion device is also disclosed in Japanese Laid-Open Patent Publication No. SHO 62-166551/1987, the device permitting the conversion between units in a combination of units absent in a memory of the device by storing a plurality of conversion rates in the memory so that the conversion rates can be used.